1. Field of the Invention
The present invention relates to backlight units and liquid crystal display devices. More specifically, the present invention relates to a backlight unit mounted on a display device such as a liquid crystal display device, and a liquid crystal display device.
2. Description of the Related Art
A liquid crystal display device is a non-self-luminous display, and therefore, it generally includes a backlight unit on the back surface of a liquid crystal display panel in order to improve display visibility. This backlight unit includes a light source and its driving circuit as components. Based on the position where the light source is arranged, such backlight units are classified into a direct backlight unit in which the light source is arranged on the lower surface of a liquid crystal display panel and a side backlight unit in which the light source is arranged on a side surface of a liquid crystal display panel. The direct backlight unit has high light use efficiency and a high luminance, and therefore it has been used in in-vehicle applications and the like for which a high luminance is needed but a slim profile is not needed. The side backlight unit has a slim profile and has high luminance uniformity, and therefore, for example, it has been used in laptop computers for which a slim profile is needed or used in display for full color images for which high image qualities are needed.
Among such backlight units, alight-emitting diode backlight unit including a light-emitting diode (hereinafter, also referred to as “LED”) as the light source has recently attracted much attention. This is because the LED backlight unit permits a reduction in costs, direct drive by a direct-current power, noise free operation, and the like. Further, an LED backlight unit including LEDs of many colors such as red (R), green (G) and blue (B) can display bright color images with high saturation.
FIG. 9A is a planar view schematically showing a configuration of a conventional side LED backlight unit. FIG. 9B is a cross-sectional view schematically showing the conventional side LED backlight unit taken along line G-H in FIG. 9A.
As shown in FIGS. 9A and 9B, according to a conventional side LED backlight unit 200, a reflective sheet 71 and a light guide plate 72 are stacked on the bottom surface of aback frame 70. Further, in an LED backlight module 68 arranged on the end surface side of the light guide plate 72, an LED 65 is arranged toward the end surface side of the light guide plate 72. Light emitted from the LED 65 is repeatedly reflected inside the light guide plate 72, and then emitted to the display surface side. According to the LED backlight unit 200 having such a configuration, as shown in FIG. 9A, LEDs 65 of a plurality of colors are connected in series for every color. The LEDs 65 are arranged from one end to the other end of the sides of the display surface at regular intervals. As shown in FIG. 9A, corners (regions shown by the dotted line) and other regions of the display surface have different light amounts from the LEDs 65 of the respective colors. Therefore, uneven color is displayed on the display surface.
Japanese Kokai Publication No. 2004-279921 specifies a display device in which a substrate is provided with an exposure part such as a through-hole so that variable electronic components are exposed in order to freely adjust the variable electronic components even after combining such a substrate with an electro-optic device. This reference discloses that a variable resistor (the variable electronic component) is adjusted and a voltage for driving liquid crystals is varied, and thereby contrast of displayed images is adjusted.